1. Field of the Invention
The present invention relates to a spacer to be used for maintaining a hermetically sealed space, and more particularly to a spacer provided in a hermetically sealed container.
2. Related Background Art
For image display there are known various image display apparatuses such as an electron beam excited display, a plasma display, a liquid crystal display and an EL display, and developments are being actively made toward a larger display image size. In such image display apparatus, a larger display image size requires a higher strength in a hermetically sealed container constituting an envelope of the image display apparatus,
As an example of such spacer, Japanese Patent Application Laid-open No. 2002-104839 discloses a spacer having a linear thermal expansion coefficient equivalent to that of soda lime silicate glass commonly employed in a face plate and a rear plate constituting a hermetically sealed container of an electron beam-excited display and still constituted of alkali-free glass. More specifically, it describes that a spacer constituted of alkali-free glass of a glass composition containing SiO2 by 10 to 35 wt %, RO (R representing an alkali earth metal) by 20 to 60 wt %, B2O3 by 9 to 30 wt % and Al2O3 by 0 to 10 wt % and substantially free from an alkali metal, employed as a spacer of the electron beam-excited display, can avoid a failure such as an electric field breakdown induced by an alkali component, and also is free from a destruction resulting from a difference in the linear expansion, since such spacer has a linear expansion coefficient equivalent to that of the soda lime silicate glass.
However, a spacer constituted of the glass of the aforementioned composition may include a bubble, that may deteriorate characteristics required for the spacer, such as a mechanical strength.